Process of chlorinating acetaldehyde



Patented May 15, 1951 PnooEss or onnomnn'rmo oETALD n Dn William Thompson Cave, Oxford, England, and Georg l n H l d, D e Rive On a Canada, assignors to Sha winigan Chemicals Limited, Montreal, Queb tion of Canada a we e a m No Drawing. Application May 2-9, 1947, Serial No. 751,474

8 Claims. 1

This invention relates to the chlorination of acetaldehyde or its polymer, para-ldehyde, and the primary object of the invention is to effect the chlorination in a rapid and efficient manner. Another object is to provide a method for producing diohloracetaldehyde, capable of continuous operation. Still another object is to provide an improved method for producing chloral in high yield and with low amounts of side reaction products. A further object is to provide a process, as aforesaid, which does not require the use of catalysts. Various other objects and advantages of the invention may be ascertained from the following description.

Processes for chlorination of acetaldehyde or paraldehyde to produce trichloracetaldehyde have been proposed but these have not been found commercially satisfactory because of low yields and the relatively large amounts of side reaction products that are produced.

Hitherto, chloral has been obtained by chlorination of ethyl alcohol. It has been suggested that the mechanism of the reaction involves the intermediate production of acetaldehyde but, in any case, acetaldehydeis not separated.

The production of chloral by chlorinationof ethyl alcohol in admixture with acetaldehydeis disclosed in French Patent No. 612,396. The reaction involves the intermediate formation of acetal, trichloracetal and chloral alcoholate. The disclosed molar ratio of water to aldehyde is 0.66 and the temperature is about 20 C., or higher.

French Patent No. 711,095 discloses a process for .chlorinating paraldehyde under anhydrous conditions. Under these conditions, paraldehyde is chlorinated without depolymerizing and the product is trichlorparaldehyde, which is immiscible with water. Monochloracetaldehyde is obtained from this by a separate depolymerizing step.

Pinner (Liebigs Annalen der Chemie, vol. 179, p. 36) obtained chloral by the chlorination of aqueous aldehyde to which pulverized marble had been added to neutralizehydrochloric acid as soon as it formed. Pinner states that a large proportion of the aqueous aldehyde was oxidized by the chlorine, and that the yield of chloral was not good. By chlorinating anhydrous paraldehyde, Pinner (Liebigs Annalen, vol. 179, .p. 21 obtained butylchloral as the major product.

'Thus, previous attempts to obtain trichlorracetaldehyde by chlorination ,of aldehyde have t r ve y e s su ll mompani d by large amounts of butylchloral and/or acetic acid and chlorinated acetic acids.

We have found that if acetaldehyde, or paraldehyde, is chlorinated in a continuous manner, in presence of amounts of Water greater than heretofore considered necessary or advisable and in successive, physically separate steps or stages each under temperature conditions different from the others and increasing from low temperature in the first stage, that almost quantitative yields of dichloracetaldehyde maybe ob.- tained at an intermediate stage of the process, while high yields of trichloracetaldehyde maybe obtained in the final stage and that in each case, only small amounts of Icy-products suchasbutylchloral and acetic acid and its chlorination'derivatilvesare produced.

For the purposes of this invention, acetaldehyde and paraldehyde are completely interchangeablef When water-immiscible paraldehyde is chlorinated according to the invention, it depolyinerizes readily during the chlorination to give water-soluble chlorinated products. When water-soluble acetaldehyde is chlorinated according to the invention, it largelypolynietiaes under the acid conditions of the reactionm'igrture, but readily depolymerizes again. Paraldehyde is the preferred starting material because it is easier to handle and store; but the invention embraces the use'of acetaldehyde both itsmonomeric form and in the form of its polymer, paraldehyde; wherefore, the term acetaldehyde as hereinafter used is to be understood as a generic term denoting both the monomeric and the paraldehyde polymeric forms, unless the context otherwise requires.

Broadly stated, the invention consists in chlorinatin'g ,acetaldehydein a continuous manner in presence of relatively large amounts of Water, in physically separate, successive steps or stages and at temperatures initially 10W and increasing from stage to stage of the process.

More particularly the invention consists in the featuresand combinations of features herein disclosed, together with all such modifications thereof and substitutions of equivalents therefor as are within the scope of the claims.

appended chlorine used, is practically quantitative and only small amounts of by-product impurities are produced. This solution of dichloracetaldehyde may be processed to yield refined dichloracetaldehyde, or the solution may be further chlorinated to produce a solution of chloral, by extending the chlorination system to a four-stage continuous process operating under favourable temperature conditions. By this procedure, the solution of dichloracetaldehyde obtained at the end of the second stage of the process goes immediately to the third stage and thence to the fourth stage, giving, as the final product of the process, a solution of chloral containing only small amounts of by-product impurities such as butyl-chloral, acetic acid and chlorinated acetic acids.

According to one manner of practising the invention, in the first stage, acetaldehyde (preferably'as paraldehyde), water and chlorine are Uniformly and continuously fed to a reacting mixture of these ingredients, which is maintained, by cooling, at a temperature within the range from about C., to about C., and preferably within the range 10 to 14 C. The molar ratio of water to acetaldehyde, or its equivalent of paraldehyde, is within the range 3.5 to 4.5 and the molar ratio of absorbed chlorine to acetaldehyde, or its equivalent of paraldehyde, is main tained within the range from about 1.5 to about 2.0; preferably between 1.6 and 1.7. The reaction mixture overflows continuously from the first stage to the second stage, where it is maintained, by cooling, at a temperature within the range from about C., to about 35 C., preferably within the range 28 to 32 C. In the second stage, the mixture is further chlorinated by continuously dispersing chlorine thereinto. chlorine absorbed in this stage is absorbed at a uniform-rate to bring the total amount of chicrine absorbed in both stages to an amount between about LB and about 2.1 mols per mol of acetaldehyde. The amount of chlorine absorbed in the. second chlorination should be at least about 0.1 mol per mol of acetaldehyde, or its equivalent of -paraldehyde.

The chlorinated solution overflows from the second stage of the process and is a solution containing a high yield of dichloracetaldehyde. By limiting the total amount of chlorine absorbed to about 2.0 mols per mol of acetaldehyde, or its equivalent of paraldehyde, there is no appreciable formation of trichloracetaldehyde. Therefore, by

' continuously operating the process, as already described, with the addition of just enough chlorine in the two stages to ensure a sufficient supply for complete chlorination of the aldehyde to dichloracetaldehyde, there is obtained a solution containing a high yield of dichloracetaldehyde with only small amounts of side reaction products, including chloral.

For the production of chloral, the reaction mixture from the second stage overflows continuously to the third stage, where it is maintained, by heating, at a temperature within the range from about 65 C., to about 75 C., preferably within the range, 69 to 71 C. Chlorine is continuously dispersed in the mixture in the third stage and the mixture is, under the prevailing conditions, further chlorinated at a rate which is substantially uniform, but which may be varied to coordinate it with the rate in the fourth stage, hereafter described. The reaction mixture overflows from the third stage to the fourth stage, where it is maintained at a temperature within the'range The from about 80 C., to about 90 C., preferably within the range, 83 to 85 C. In this last stage, chlorine is continuously dispersed in the mixture, which is, under the prevailing conditions, further chlorinated at a rate adjusted so'that the dichloracetaldehyde content of the mixture overflowing from the fourth stage is maintained below about 3%, as. determined by periodic analyses.

The'relative rates of chlorine addition in the third and fourth stages should be, preferably, in the ratio within the range from about 0.4 to about 1.0. The chlorine content of the vent gases from the fourth stage should not exceed about 35% and, preferably, should not exceed.20%. However, if the rate of chlorination in the fourth stage which gives this content of chlorine in the vent gases does not hold the dichloracetaldehyde content of the effluent reaction mixture down to 3%, the chlorine input to the third stage should be increased.

Alternatively, the reaction mixture overflowing from the second stage may be chlorinated in batches. The chlorination is started while the reaction mixture is at the temperature at which it overflows from the second stage and the temperature of the batch is raised gradually. The rate of chlorine addition is regulated according to the rate of temperature rise, so that chlorine is added as rapidly as it is absorbed by the systern, excess chlorine being vented in the vent gases and not exceeding 5% of these gases. The chlorination is finally completed when the reaction mixture reaches the same final temperature range used in the continuous process and, as before, the criterion of completion is that the dichloracetaldehyde content shall be less than about 3%. As the chlorination nears completion, the excess chlorine content of the vent gases may be allowed to rise to about 35%.

, Refined dichloracetaldehyde may be obtained from the solution overflowing from the second stage of the process, by most of the methods usually used for refining crude chloral. Refined chloral may be obtained by any suitable process from the crude trichlorination product of the process.

The following example is further explanatory of the carryin out of the process but it is to be understood, the invention is not limited to the details thereof.

. ExampZa-Water and acetaldehyde in the form of paraldehyde, in the molar ratio, 4.24:1, were fed continuously, along with chlorine in the molar ratio, chlorinezacetaldehyde, of 1.88:1, into a reaction vessel full of these ingredients previously reacted. The contents of the vessel was maintained at a temperature within the range, 10 C., to 12 C., by cooling. Material overflowing from the reaction vessel, as reactants were- About 98% of the chlorine fed to these two vessels 7 was absorbed, the remainder being lost in the vent gases, which were not recycled for recovery terial was further chlorinated in batches.

based on the aldehyde used, were mechanical,

and were due to uncondensed vent gases which contained appreciable amounts of chlorinated aldehyde.

The reaction rates in the initial stages of the chlorination of acetaldehyde or paraldehyde, as aforesaidappear to be so rapid that the hold-up time required in these stages is a function of the mechanics of the process rather than of the chemistry of the process. The basic factor influencing the chlorination rate in all stages is the efficiency of the gaseous chlorine dispersion in the liquid mass. The more efiicient the gas dispersion, the shorter will be the hold-up time required in each stage. Within the limits prescribed for the various stages, temperature has practically no effect on the reaction rate. Since the reaction rates are not controlling factors in the first and second stages, the hold-up times required in these stages will be governed by the capacity of kettles, heat exchangers, and

other elements of apparatus used. The reaction rates in the third and fourth stages are much slower than in the first and second stages, wherefore, the hold-up time required will depend on the efficiency of the chlorine dispersion method used. Using modern, efiicient, gas dispersion systems, the hold-up time in the third and fourth stages can be of the same order of magnitude as in the first and second stages.

As herein outlined, this process of chlorinating acetaldehyde requires no catalyst unless water is regarded as a catalyst. The water used to dilute the aldehyde serves to suppress undesirable side reactions, such as the formation of butylchloral. Water has previously been used as a reaction promoting substance in the chlorination of acetaldehyde or paraldehyde to chloral, but its use as a diluent and in the large proportions herein described, is believed to be entirely new.

The advantages of continuous chlorination, especially in the initial stages of the process, are more than those which normally accrue from the change in a chemical process from batch operation to continuous operation. In the process of this invention, the production of butylchloral and acetic acid and its chlorination derivatives is sharply decreased as compared with the production of these by-products in batch chlorinations of acetaldehyde or paraldehyde.

In a batch process, by the use of large amounts of hydrochloric acid in the initial chlorination charge, only small amounts of acetic acid are produced but relatively large amounts of butylchloral will be simultaneously produced. Also, by the use of low temperatures and dilute aldehyde, only small amounts of butylchloral but relatively large amounts of acetic acid will be produced.

It is only in the process of this invention, wherein chlorination is carried out continuously 6. in the first and second stages, that production of both butylchloral and acetic acid and its chlorination derivatives can be restricted to small quantities.

Having thus described our invention, we claim:

1. A process of chlorinating acetaldelhyde, which process comprises; continuously feeding water, acetaldehyde and chlorine into a reacting mixture of the same held at a temperature within the range between about 5 C., and about 15" C., the molar ratio of water to aldehyde being between about 3.5 and about 4.5 with chlorination of the aldehyde, the molar ratio of chlorine absorbed to aldehyde fed being between about 1.5 and about 10; continuously collecting reacting mixture overflowing from said chlorination reaction and continuously dispersing chlorine into said collected overflow reaction mixture, while maintaining a temperature within. the range between about 25 C., and about 35 C., with further absorption of chlorine to such an extent that the total absorbed in both chlorinations combined does not exceed about 2;0 mols per mol of aldehyde.

2. A process of chlorinating acetaldehyde, which process comprises; continuously feeding water, acetaldehyde and chlorine into a reacting mixture of the same held at a temperature within the range between about 5 C., and about 15 C., the molar ratio of water to aldehyde being between about 3.5 and about 4.5, with .chlorination of the aldehyde, the molar ratio of chlorine absorbed to aldehyde fed being between about 1.5 and about 2.0; continuously collecting the reaction mixture overflowing from said ch10 rination reaction and continuously dispersing chlorine into said collected overflow reaction mixture, while maintaining a temperature within the range between about 25 C., and about 35 C., with further absorption of chlorine to bring the total amount of chlorine absorbed to within the range between about 1.9 and about 2.2 mols of chlorine per mol of acetaldehyde, at least 0.1 mol of chlorine per mol of acetaldehyde being absorbed in the second chlorination.

3. A process of chlorinating acetaldehyde, which process comprises; continuously feeding water, acetaldehyde and chlorine into a reacting mixture of the same held at a temperature within the range between about 5 C., and about 15 C., the molar ratio of water to aldehyde being between about 3,5 and about 4.5, with chlorination of the aldehyde, the molar ratio of chlorine absorbed to aldehyde fed being between about 1.5 and about 2.0; continuously collecting the reaction mixture overflowing from said chlorination reaction and continuously dispersing chlorine into said collected overflow reaction mixture, while maintaining a temperature within the range between about 25 C., and about 35 C., with further absorption of chlorine to bring the total amount of chlorine absorbed to within the range between about 1.9 and about 2.2 mols of chlorine per mol of acetaldehyde, at least 0.1 mol of chlorine per mol of aldehyde being absorbed in the second chlorination; continuously collecting the reaction mixture overflowing from the second chlorination reaction and continuously dispersing chlorine into said collected overflow reaction mixture, while maintaining a temperature within the range between about 65 C., and about 75 C., with further absorption of chlorine; continuously collecting the reaction mixture overflowing from said third chlorinathe dichloracetaldehyde content of the resultingchlorinated mixture overflowing from the fourth chlorination does not exceed 3%, the relative rates of chlorine feed to the third and fourth chlorination being in a ratio within the range between about 0.4 and about 1.0.

4. A process of chlorinating acetaldehyde, which process comprises; continuously feeding water, acetaldehyde and chlorine into a reacting mixture of the same, held at a temperature within the range between about 5 0., and about 15 C., the molar ratio of water to aldehyde fed being between about 3.5 and about 4.5, with chlorination of the aldehyde, the molar ratio of chlorine absorbed to aldehyde fed being between about 1.5 and about 2.0; continuously collecting the reaction mixture overflowing from said chlorination reaction and continuously dispersing chlorine into said collected overflow reaction mixture, while maintaining a temperature within the range between about 25 C., and about 35 C., with further absorption of chlorine to bring the total amount of chlorine absorbed to within the range-between about 1.9 and about 2.2 mols of chlorine per mol of aldehyde, at least 0.1 mol of chlorine per mol of aldehyde being absorbed in the second chlorination; collecting the reaction mixture overflowing from the second chlorination reaction into batches; raising the temperature of each successive batch, after it has been collected, to a temperature in the range between about 80 C.,-and about (3,, while dispersing chlorine into the batch as rapidly as it is absorbed, and continuing the dispersion of chlorine into each batch at its maximum temperature until the dichloracetaldehyde content of the batch falls below about 3%.

5. A process as in claim 1, in which the acetaldehyde is in the polymeric paraldehyde form.

6. A process as in claim 3, in which the acetaldehyde is in the polymeric paraldehyde form.

7. A process as in claim 3, in which the acetaldehyde is in the polymeric paraldehyde form.

8. A process as in claim 4, in which the acetaldehyde is in the polymeric paraldehyde form.

WILLIAM THOMPSON CAVE. GEORGE ERLING HADDELAND.

REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENT Number Name Date 1,620,180 Young et al. Mar. 8, 1927 2,443,183 Cass June 15, 1948 2,478,741 Brothman Aug, 9, 1949 OTHER REFERENCES Annalen, vol. 179180 

1. A PROCESS OF CHLORINATING ACETALDEHYDE, WHICH PROCESS COMPRISES; CONTINUOUSLY FEEDING WATER, ACETALDEHYDE AND CHLORINE INTO A REACTING MIXTURE OF THE SAME HELD AT A TEMPERATURE WITHIN THE RANGE BETWEEN ABOUT 5* C., AND ABOUT 15* C., THE MOLAR RATIO OF WATER TO ALDEHYDE BEING BETWEEN ABOUT 3.5 AND ABOUT 4.5 WITH CHLORINATION OF THE ALDEHYDE, THE MOLAR RATIO OF CHLORINE ABSORBED TO ALDEHYDE FED BEING BETWEEN ABOUT 1.5 AND ABOUT 1.9; CONTINUOUSLY COLLECTING REACTING MIXTURE OVERFLOWING FROM SAID CHLORINATION REACTION AND CONTINUOUSLY DISPERSING CHLORINE INTO SAID COLLECTED OVERFLOW REACTION MIXTURE, WHILE MAINTAINING A TEMPERATURE WITHIN THE RANGE BETWEEN ABOUT 25* C., AND ABOUT 35* C., WITH FURTHER ABSORPTION OF CHLORINE TO SUCH AN EXTENT THAT THE TOTAL ABSORBED IN BOTH CHLORINATIONS COMBINED DOES NOT EXCEED ABOUT 2.0 MOLS PER MOL OF ALDEHYDE. 